Well, i love touhou because of it's incredible cast of characters, each with their unique abilites and stories. I also love how each of the games have a somewhat surreal and relaxing atmosphere, especially touhou 6, combine that with the awesome music that really makes you feel all sorts of different emotions. And then of course we have the large amounts of amazing fanworks, tho i'm not really interested in them.
And nothing, touhou is and will remain my favourite game series and it will be a real shame when it will reach its eventual end.